This paper introduces the hardware structure, software design and specific implementation of speed regulation scheme of brushless DC motor controller based on PIC16F873A.
This controller adopts current single closed-loop control strategy and PWM speed regulation mode to control brushless DC motor.
The validation shows that the controller has simple structure, stable and reliable performance and good speed regulation effect. PIC16F873A is a high performance mid-range microcontroller with RISC structure produced by Microchip Company.
The stability of the single chip computer is good, and the anti-transient ability of the pin provides a stable guarantee for the system. Because the chip is cheap and stable, the speed control system of brushless DC motor based on PIC16F873A is of practical application value.
The system adopts single closed-loop current and two-two-conductor commutation control mode, and designs under-voltage, thermostatic element over-current, blocking and other protection modes. It has been proved by long-term practice that the system has high reliability, strong anti-interference ability and simple hardware design. The hardware block diagram of the system is shown in Figure 1. The main circuit of the system is shown in Figure 2. The main circuit of three-phase power bridge is composed of six IGBT FGA25N120. In this control system, the rated voltage of the motor is 100V and the rated current is 3A. FGA25N120 has a maximum operating voltage of 1200V and a maximum current of 25A, which fully meets the requirements of the system. In Figure 2, the full bridge structure can improve the utilization ratio of motor windings. By controlling the switching and switching of six power, the voltage and current waveforms of the motor are adjusted to produce continuous torque for BLDCM. The advantage of adding a sampling resistor RS in the main circuit is that the Hall current sensor can be omitted and the circuit structure is simpler. The purpose of incorporating resistance R at G and S ends of power transistors is to prevent the power transistors from burning down due to the current when they are suspended. The isolation driving circuit is an isolation driving circuit for the lower and lower arm of the bridge along the road, which drives a group of upper and lower power transistors. The input signals A1 and A1 are output from GAL16V8. The PWM modulation mode of the system is chopper for the lower bridge, and A1 is the PWM signal through chopper. The current signal taken from the sampling resistance is shown in Fig. 3. Because of the possibility of positive and negative, because the system sampled two-two-on commutation mode, there are only two power transistors working at every 60 degree electric angle, i.e. only two-phase windings are on, it is possible to generate reverse current when the windings commutate or when the bridge chops down. At this time, the current is not what we want to detect. Only the forward current is what we want. Therefore, a diode D4 is added to the circuit figure 3 so that the detected current IA can only flow through the forward current. The motor speed regulation of this system is realized by adjusting the duty cycle of PWM wave of TL494 output by controlling the dead time of TL494 after filtering the output PWM wave of PIC. Potentiometer DWQ1 adjusts the given voltage so that the voltage is within the range of sawtooth wave voltage generated in TL494, and forms a closed-loop system with the detected current, thus PI regulation is carried out. The purpose of this potentiometer is to make TL494 chopper and form current closed loop. The system has the protection of temperature, over current and lack of phase. Temperature switch is used to detect the temperature of IGBT.
Once the temperature exceeds 75 C, the temperature switch closes and outputs high level to PIC. The system stops. When the system is over-current, the detected current signal is transformed into voltage signal by resistance and compared with the potentiometer setting value. When the upper limit value is exceeded, the comparator outputs high level to PIC, and the system loses power, thus the system is protected. The system also has phase-absence protection, that is, when the detected position Hall signal is disconnected, the system will stop and there will be fault indication. The output signals of position sensors are 101, 001, 011, 010, 110 and 100. Thus, by capturing the jump edge of any output of Hall sensor and reading the output state of Hall sensor after the jump edge, the new position of the rotor can be determined and the current commutation of the stator winding can be realized. The software of the controller refers to the application program for PIC16F873A chip. The main program of the controller includes initialization of the controller, charging delay program of the main circuit, programming language realization of control algorithm, design of interruption flow, etc.
The controller of BLDCM based on PIC16F873A has simple structure, stable and reliable performance and good speed control effect. In the process of operation, the brushless DC motor can start fast, run smoothly and has low noise.
It can meet the practical application needs of household appliances, medical, textile and other industries.